Use of Statistical Parameters in the Sedimentological ...

IOSR Journal of Applied Geology and Geophysics (IOSR-JAGG)

e-ISSN: 2321–0990, p-ISSN: 2321–0982.Volume 1, Issue 5 (Nov. – Dec. 2013), PP 21-27 www.iosrjournals.org

www.iosrjournals.org 21 | Page

Use of Statistical Parameters in the Sedimentological Study of

Conglomerate Deposits in Northeastern Part of Akwa Ibom State,

Niger Delta Basin, Nigeria

Udo, I. G.1, Mode, A. W.

2

1Department of Geology, University of Nigeria, Nsukka, Nigeria. 2Depatment of Geology, University of Nigeria, Nsukka, Nigeria.

Abstract: Conglomerates and pebbly sandstone abound along a belt of about 50km long and 11km wide in

northeastern part of Akwa Ibom State. Granulometric analysis of 29 samples show the deposits to be poorly to

moderately sorted, having sorting coefficient values ranging between 0.63ф to 1.41ф. Pebble morphometric

analysis of the conglomerates showed that the mean values of the various morphometric parameters range as

follows: flatness ratio (S/L = 0.39-0.58), elongation ratio (I/L =0.64-0.78), maximum projection sphericity (Ψ P

= 0.60-0.77), Oblate Prolate index (Ō P = -1.98 to 4.13), coefficient of flatness (39.25-57.86). Roundness index

determined for the pebbles through simple comparism with Power’s (1953) roundness chart averaged 0.232. Interpretation of pebble morphometric and granulometric results indicate a fluvial environment of deposition

for the deposits.

Keywords: Conglomerate, deposit, environment, fluvial, roundness

I. Introduction A belt of conglomerate showing a northwest-southeast trend covers an area of about 550km2 in

northeastern part of Akwa Ibom State. The Conglomerate deposits cut across Itu, Ini, Ikono, Ibiono Ibom, Uyo

and Uruan Local Government Areas of Akwa Ibom State. The environment of deposition of the deposits has

been controversial. Amajor (1986) studied the conglomerate deposit in Itu Local Government Area of the State

and interpreted the deposits to be of alluvial fan origin. Petters (1989) also worked on the conglomerate deposit in Itu and Ikono Local Government Areas of the State and suggested a beach environment (marginal marine

setting) for the deposits. However, there is no regional view of the conglomerate deposits. The aim of this work

is to determine the depositional setting of the conglomerate deposits based on regional study.

II. Geology of the Study Area The study area is bounded by Longitude 70 401E-80 001E and Latitude 50 011N-50 301N.

Stratigraphically, the deposits belong to Ameki Formation. Reyment (1965) described Ameki Formation as a

series of highly fossiliferous grey-green sandy clays with calcareous concretions and white clayey sandstones.

The lower part consists of fine to coarse sandstones and intercalations of calcareous shale and thin, shelly limestone, the upper with coarse, cross-bedded sandstones, bands of fine sandstones and sandy clays. It is

locally rich in Molluscs, foraminifera and Ostracods. Lithologically, Ameki Formation is very heterogeneous

(Wilson, 1925; Reyment, 1965; Adegoke, 1969). Arua and Rao, 1986 noted the presence of pebbles in Ameki

Formation. Agagu et. al (1985) and Petters (1978) have interpreted the Ameki Formation to be Estuarine,

Lagoon and open marine setting. The Ameki Group consists of the Nanka sand, Nsugbe Formation and Ameki

Formation (Nwajide, 1979). The Formation has been considered to be either Early Eocene (Reyment, 1965) or

early to Middle Eocene (Berggren, 1960; Adegoke, 1969) and deposited in estuarine, lagoonal and open marine

environment content. White (1926) assigned an estuarine environment because of the presence of fish species of

known estuarine affinity. Adegoke (1969), however, indicated that the fish were probably washed into the

Ameki sea from inland waters, and preferred an open marine depositional environment. Nwajide (1979) and

Arua (1986) suggested environments that ranged from nearhore (barrier ridge-lagoonal complex) to intertidal and subtidal zones of the shelf environment, whereas Fayose and Ola (1990) suggested that the sediments were

deposited in marine waters between the depth of 10m to 100m. According to Nwajide and Reijers (1996), the

progradational Nanka Formation marks the return to regressive conditions. The outcropping deposits of the

Eocene regression, which marks the beginning of the Niger Delta progradation, constitute the Ameki Group,

which include the tidal facies and backshores as well as pro-delta facies. The prograding shoreface and river

deposits are reflected in the subsurface deposits of Agbada Formation in the Northern depobelts of the Niger

Delta.

Use Of Statistical Parameters In The Sedimentological Study Of Conglomerate Deposits In


fig.1. geological map showing the study area

III. Methodology Representative samples of the various lithologic units were collected from outcrops in the study area.

Each was disaggregated and sieved through 4mm screen to separate the gravels from sand for pebble

morphometric analysis and granulometric analysis respectively. Computation of maximum projection sphericity (Ψ P), Oblate Prolate index (Ō P ), coefficient of flatness, inclusive graphic skewness, inclusive graphic

standard deviation, graphic kurtosis, and mean grain size were done using appropriate formulae. Qualitative

estimate of the Roundness of the pebbles was noted through simple comparison with Power Roundness chart

(After Power,1953).

IV. Result The mean values of the various morphometric parameters range as follows: flatness ratio (S/L = 0.39-

0.58), elongation ratio (I/L =0.64-0.78), maximum projection sphericity (Ψ P = 0.60-0.77), Oblate Prolate index

(Ō P = -1.98 to 4.13), coefficient of flatness (39.25-57.86), roundness = 0.232 (TABLE 1). Considering the mean geometric forms, 72% of the samples were bladed, 22% were compact bladed and 6% were compact

elongate (TABLE 1).

From the granulometric results of 29 samples (TABLE 2), the skewness values indicate that 62.1% of

the samples are positively skewed, 27.6% are symmetrical, while 10.3% are negatively skewed. The kurtosis

values indicate that 31% of the samples are leptokurtic, 38% mesokurtic and 31% platykurtic. Sorting values

indicate that 96.6% of the samples are poorly sorted while 3.4% is moderately sorted.



TABLE 1: Mean Values of Pebbles Measured SAMPLE

NUMBER

𝑰

𝑳

𝑺

𝑳

𝑳 − 𝑰

𝑳 − 𝑺

ΨP OP COEFFICIENT

OF FLATNESS

FORM MEAN

ROUNDNESS

IN25S2 0.6566 0.4779 0.6539 0.6833 3.4550 47.78 B 0.250

IN4S1 0.6986 0.3935 0.5022 0.5992 -0.1503 39.25 B 0.219

IN5S1 0.7349 0.4755 0.5257 0.6744 0.0816 47.55 B 0.255

IN8S2 0.7411 0.4874 0.5015 0.6842 -0.1746 48.74 B 0.223

IN10S3 0.7343 0.4948 0.5289 0.6912 0.5297 49.48 B 0.222

IN27S1 0.7124 0.4060 0.4960 0.6150 -0.5458 40.60 B 0.245

IK2S1 0.7341 0.4709 0.5046 0.6685 0.0680 47.09 B 0.223

IB7S1 0.7728 0.5160 0.4604 0.6958 0.7556 51.60 CB 0.233

IB12S1 0.7691 0.4779 0.4389 0.6648 -1.3145 47.79 B 0.230

IB8S1 0.7316 0.4587 0.4879 0.6601 -0.0922 45.87 B 0.252

IN12S2 0.6737 0.4603 0.6007 0.6792 2.3940 46.03 B 0.222

IN7S1 0.6957 0.4577 0.5531 0.6652 1.4920 45.77 B 0.223

IN16S2 0.7379 0.4874 0.5193 0.6806 0.3104 48.74 B 0.223

IT1S1 0.6815 0.4720 0.6026 0.6860 2.3569 47.20 B 0.232

IB4S1 0.7210 0.5044 0.5459 0.7044 1.1715 50.44 CB 0.237

IK1S2 0.7207 0.4940 0.5609 0.6934 1.1023 49.40 B 0.236

IB2S1 0.6453 0.4613 0.6694 0.6882 3.5278 46.17 B 0.239

IB9S1 0.6815 0.4537 0.5888 0.6689 1.8027 45.37 B 0.242

IT2S1 0.7096 0.5166 0.6042 0.7207 2.0755 51.66 CB 0.244

UR1S1 0.6814 0.4653 0.6040 0.6780 2.1505 46.53 B 0.244

IB10S1 0.6567 0.4563 0.6380 0.6824 3.0401 45.63 B 0.235

IT5S2 0.6984 0.4583 0.5846 0.6652 1.4480 45.83 B 0.240

IN26S1 0.7066 0.4845 0.5959 0.6983 1.8147 48.45 B 0.230

IB3S1 0.7153 0.4620 0.5151 0.6636 0.2526 46.20 B 0.232

UR2S1 0.7587 0.4263 0.4194 0.6208 -1.9848 42.63 B 0.229

UY1S1 0.7018 0.4516 0.5499 0.6562 1.1273 45.16 B 0.233

IT4S1 0.7051 0.4578 0.5516 0.6746 0.9352 45.78 B 0.247

IB18S1 0.6575 0.4598 0.6327 0.6853 2.9708 45.98 B 0.231

IB17S1 0.6840 0.4746 0.6153 0.6887 2.2032 47.46 B 0.234

IB16S1 0.7064 0.4698 0.5437 0.6762 1.2124 46.98 B 0.239

IB15S1 0.7380 0.4812 0.4929 0.6785 0.1589 48.12 B 0.224

IN13S6 0.6448 0.4187 0.6152 0.6452 2.7881 41.87 B 0.237

IN14S1 0.7565 0.4797 0.4911 0.6701 -0.6787 47.97 B 0.238

IN11S4 0.7010 0.4107 0.5213 0.6193 0.1173 41.07 B 0.235

IN9S5 0.7402 0.4696 0.4945 0.6664 -0.2126 46.96 B 0.227

IB5S1 0.7176 0.4668 0.5284 0.6698 0.6953 46.68 B 0.231

IN6S1 0.7312 0.4847 0.5351 0.6827 0.5527 48.42 B 0.231

IB6S1 0.7775 0.4879 0.4441 0.6736 -1.4001 48.79 B 0.235

IN1S1 0.7119 0.4542 0.5276 0.6620 0.6668 45.42 B 0.230

IN3S6 0.7308 0.4611 0.5073 0.6592 0.0176 46.11 B 0.230

IN2S1 0.6567 0.5157 0.7052 0.7410 4.1315 51.57 CE 0.220

IN17S1 0.7367 0.5428 0.5645 0.7341 1.3996 54.28 B 0.224

IK3S1 0.6822 0.5013 0.6417 0.7190 2.7856 50.13 CB 0.223

IN15S1 0.7103 0.5743 0.6945 0.7706 3.3114 57.43 CE 0.217

IT6S2 0.6836 0.5322 0.6853 0.7444 3.4272 53.22 CE 0.226

IT3S4 0.7083 0.5406 0.6316 0.7440 2.5377 54.06 CB 0.224

IB13S5 0.7191 0.5529 0.6286 0.7504 2.4204 55.29 CB 0.227

IB14S2 0.7136 0.5467 0.6258 0.7424 2.4082 54.67 CB 0.225

IB11S2 0.7710 0.5786 0.5467 0.7542 0.7908 57.86 CB 0.221

IB20S2 0.7391 0.5515 0.5803 0.7437 1.4694 55.15 CB 0.224



B – Bladed CB – Compact Bladed CE – Compact Elongate

TABLE 2. Grain Size Parameters

SAMPLE Ф5 Ф16 Ф25 Φ50 Φ75 Φ84 Φ95 Mz σ₁ SKı KG REMARK

IB6S1 -0.85 -0.42 -0.20 0.50 1.38 1.60 2.30 0.56 0.98 0.12 0.82 MS,PK,P

IN7S1 -0.66 -0.27 -0.05 0.57 1.30 1.65 2.35 0.65 0.94 0.15 0.91 MS,PK,M

IN4S5 -0.94 -0.40 -0.05 0.60 1.00 1.58 2.45 0.59 1.01 0.04 1.32 PS,S,L

IB8S1 -0.68 -0.12 0.20 1.10 2.05 2.40 3.30 1.13 1.23 0.07 0.88 PS,S,P

IN6S1 -0.91 -0.40 -0.15 0.66 1.68 2.15 3.20 0.80 1.26 0.20 0.92 PS,PK,M

IB2S2 -0.64 -0.05 0.40 1.15 1.50 1.80 2.43 0.97 0.93 -0.23 1.14 MS,NK,L

IN16S2 -0.80 -0.42 -0.21 0.35 1.15 1.50 2.25 0.48 0.94 0.22 0.92 MS,PK,M

IB5S1 -0.95 -0.21 0.10 0.60 1.25 1.55 2.10 0.65 0.90 0.03 1.09 MS,S,M

IB14S2 -0.7 -0.37 -0.15 0.60 1.50 1.90 2.80 0.71 1.10 0.20 0.87 PS,PK,P

IN25S2 -0.93 -0.30 0.00 0.64 1.30 1.65 2.30 0.66 0.98 0.03 1.02 MS,S,M

IN10S3 -0.80 -0.43 -0.25 0.18 0.76 1.00 2.00 0.25 0.78 0.22 1.14 MS,PK,L

IN14S1 -0.63 -0.33 -0.18 0.40 0.89 1.40 2.64 0.49 0.93 0.26 1.25 MS,PK,L

IN2S2 -0.63 0.04 0.38 0.84 1.57 1.84 2.89 0.91 0.98 0.14 1.21 MS,PK,L

IK4S1 -0.20 0.30 0.45 0.88 1.35 1.65 2.45 0.94 0.74 0.16 1.21 MS,PK,L

IN26S1 -0.98 -0.46 -0.20 0.40 1.30 1.75 2.64 0.56 1.10 0.23 0.99 PS,PK,M

IN1S2 -0.97 -0.50 -0.30 0.40 1.39 2.16 2.75 0.69 1.23 0.29 0.90 PS,PK,M

IT5S3 -0.64 -0.37 -0.20 0.38 1.10 1.40 2.25 0.47 0.88 0.22 0.91 MS,PK,M

UR2S1 -0.45 0.55 1.20 2.60 3.10 3.24 3.48 2.13 1.27 -0.54 0.85 PS,VNK,P

IT3S4 0.15 0.43 0.59 1.05 1.50 1.72 2.17 1.07 0.63 0.07 0.91 MWS,S,M

IB13S5 -0.93 -0.35 -0.05 0.65 1.50 2.10 3.14 0.80 1.23 0.20 1.08 PS,PK,M

IB7S1 -0.87 -0.42 0.03 0.82 1.50 1.65 1.98 0.68 0.95 -0.19 0.79 MS,NK,P

IN17S1 -0.77 -0.27 0.00 0.94 2.25 2.80 3.50 1.16 1.41 0.21 0.78 PS,PK,P

IN8S2 -0.92 -0.39 -0.10 -0.60 1.14 1.54 2.50 0.18 1.00 1.02 1.13 PS,PK,L

IK2S1 -0.66 -0.19 0.00 0.86 1.64 1.93 2.60 0.87 1.02 0.04 0.81 PS,S,P

IN12S6 -0.92 -0.35 0.05 0.70 1.50 2.05 3.10 0.80 1.21 0.16 1.14 PS,PK,L

IN13S6 -0.77 -0.38 -0.20 0.35 1.14 1.46 2.20 0.48 0.91 0.23 0.91 MS,PK,P

IB4S1 -0.85 -0.25 -0.10 0.80 1.40 1.64 2.27 0.73 0.95 -0.08 0.85 MS,S,P

UR1S1 -0.68 -0.37 -0.23 0.12 1.00 1.34 2.05 0.36 0.84 0.42 0.91 MS,VPK,M

IT2S1 -0.82 -0.28 1.00 0.70 1.40 1.70 2.48 0.71 1.00 0.04 3.38 PS,S,EL

Legend

PS – Poorly sorted NK – Negatively skewed L – Leptokurtic

MS – Moderately sorted VPK – Very positively skewed EL – Extremely leptokurtic

MWS – Moderately well sorted VNK – Very negatively skewed S - Symmetrical

PK – Positively skewed P – Platykurtic M - Mesokurtic

V. Discussion According to Dobkin and Folk (1970), Gale (1990), particular gravel clasts shape concentrate in

particular environments. For example Disc accumulates on beaches while rollers (Elongate clasts) and Bladed

accumulate in rivers. From the result (TABLE 1), 72% of the samples were Bladed, 22% were compact Bladed,

6% were compact Elongate. Since the mean geometric form were Bladed, compact Bladed, and compact

Elongate (Fig.3), it means that the environment of deposition is likely to be fluviatile.

In a comperative study of gravels obtained from beaches and rivers in Southern Africa, Stratten (1974)

found that fluvial pebbles have mean coefficient of flatness of more than 45 and that their mean sphericities

exceeds 0.65. Dobkin and Folk (1970), in their study of basalt pebbles in rivers and beaches in Tahiti-Nui,

arrived at a lower limit of 0.66 for the mean sphericity of fluvial pebbles, a figure very close to that of stratten

(1974). Dobkin and Folk (1970), also found that the mean Oblate-Prolate index of fluvial pebbles exceeds -1.5,

whereas the value of beach pebbles is lower. It seems, therefore, that the following values are approximate lower index limits for pebbles shaped in a fluvial environment:

Sphericity 0.65

Coefficient of flatness 45

Oblate-Prolate index -1.5

From the result, the means of the above three indices for almost all the localities are well above the

lower limits for fluvial pebbles thus lending credence to fluvial origin.

Plot of maximum projection sphericity against coefficient of flatness(Fig.2) shows that majority of the

points lie in the fluvial field of Stratten (1974).

Bivariate plot of maximum projection sphericity versus Oblate-Prolate index (Fig.4) also shows most

of the points plotting within the fluvial realm.

Sames (1966) found that roundness values less than 0.350 are typical of river pebbles whereas values more than 0.450 suggest littoral environment. Dobkin and Folk (1970) established for river and beach pebbles,



mean roundness values of 0.375 and 0.508 respectively. From these values, it appears that a mean roundness

index of 0.380 is the upper limit for pebbles shaped by a river.

The mean roundness value for pebbles in the study area calculated from TABLE 1 is 0.232. This is well below the critical value of 0.380 for river pebbles.

According to McManus (1995), beach sands are well sorted and negatively skewed while river sands

are less well sorted and usually positively skewed. From the granulometric result (TABLE 2), the sorting values

indicate that 96.6% of the samples are poorly sorted while 3.4% is moderately well sorted. The skewness values

indicate that 62.1% of the samples are positively skewed, 27.6% are symmetrical, while 10.3% are negatively

skewed. The poorly sorted nature of the samples and the positively skewed nature of most of the samples

support fluvial origin.

Bivariate plots of skewness versus sorting (Fig.6) and mean grain size versus sorting (Fig.5) indicate

that the environment of deposition is fluvial (Friedman 1967, Moiola and Weiser 1968).

fig.2. plot of coefficient of flatness versus ψp after Stratten, 1974

0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Series1

RIVER

BEACH

MAXIMUM PROJECTION SPHERICITY (ψp)

CO

EFFI

CIE

NT

OF

FLA

TNES

S



fig. 3. sphericity form diagram after Sneed and Folk (1970). each point is an average of twenty pebbles.

fig. 4. plot of ψp versus OP after Dobkin and Folk (1970)

fig. 5. plot of mean grain size versus sorting after Moiola and Weiser, 1968



fig. 6. plot of skewness versus sorting after Friedman, 1967

VI. Conclusion

This study reveals that the conglomerate deposits in Northeastern part of Akwa Ibom State, Niger Delta

basin, Nigeria are of fluvial origin.

Acknowledgement We are grateful to Udom, G. J. for his helpful comments.

References

[1]. L. C. Amajor, Alluvial fan Facies in the Miocene-Pliocene coastal plain sand, Niger Delta, Nigeria, Journal of Sedimentary

Geology, 49, 1986, 1- 20.

[2]. S. W. Petters, Akwa Ibom State Physical Background, Soils and Land use Ecological Problems, Technical Report of the Task

Force on Soil and Land Use Survey, Akwa Ibom State ( Government Printers, Uyo, 1989).

[3]. R. A. Reyment, Aspects of the Geology of Nigeria, (Ibadan University Press, Ibadan, 1965).

[4]. R. C. Wilson, The geology of th Eastern Railway, Section 1, Port Harcourt to Enugu, Geolological Survey of Nigeria Bullettin, 8

1925, 1-95.

[5]. O. S. Adegoke, Eocene stratigraphy of southern Nigeria, Bull. B. R.G.M. Mem. .69, 1969, 23-48.

[6]. I. Arua, V. R. Rao, New stratigraphic data od Eocene Ameki Formation, Southeastern Nigeria., Journal of African Earth Science,

3, 1986, 1-7.

[7]. O. K. Agagu, E. A. Fayose and S. W. Petters, Stratigraphy and Sedimentation in the Senonian Anambra Basin of Eastern

Nigeria, Nigerian Journal of Mining and Geology, 22, 1985, 25-36.

[8]. S. W. Petters, Stratigraphic Evolution of the Benue Trough and its Implications for the Upper Cretaceous Paleogeograhy of West

Africa, Journal of Geology, 86, 1978, 311-322.

[9]. C. S. Nwajide, A lithostratigraphic analysis of the Nanka Sands, southeastern Nigeria., Nigerian Journal of Mining and

Geology,16, 1979, 103-109.

[10]. W. A. Berggren, Paleocene Biostratigraphy and Planktonic Foraminifera of Nigeria (West Africa), Proc. 21st Inter. Geol. Cong.

Copenhagen, 6, 1960, 41-55.

[11]. E. L. White, Eocene fishes from Nigeria, Bullettin of Geological Survey of Nigeria 10, 1926, 1-82.

[12]. I. Arua, Paleoenvironment of Eocene deposits in Afikpo syncline, southern Nigeria, Journal of African Earth Science, 5, 1986,

279-284.

[13]. E. A. Fayose and P. S. Ola, Radiolarian occurrences in the Ameki type section, eastern Nigeria, Journal of Mining and Geology

26, 1990, 75-80.

[14]. C. S. Nwajide and T. J. A. Reijers, Geology of the southern Anambra Basin. In: Reijers, T. J. A. (Ed), selected chapters on

geology: Sedimentary geology and sequence stratigraphy of Anambra Basin (SPDC Corporate Reprographic Services, Warri,

Nigeria, 1996) 133-148.

[15]. M. C. Power, A New roundness Scale for Sedimentary Particles, Journal of Sedimentary Petrology, 23, 1953, 117-119. Petrol., 23,

p. 117-119.

[16]. J. Dobkins and R. K. Folk, Shape Development on Tahiti-Nui, Journal of Sedimentary Petrology, 40 (4), 1970, 1167-1203.

[17]. S. J. Gale, The Shape of Beach Gravels, Journal of Sedimentary Petrology, 60, 1990, 787-789.

[18]. T. Stratten, Notes on the Apllication of Shape Parameters to Differentiate between Beach and River Deposits in Southern Africa.

In: Pebble Morphology of Ancient Conglomerate. The Middlevlei Gold Placer, Witwatersrand, South Africa (ed. B. G. Els),

Journal of Sedimentary Petrology, 58, 1974, 894-901.

[19]. C. Sames, Morphometric Data of Some Recent Pebble Association, Journal Sedimentary Petrology, 36. 1966, 126-142.

[20]. J. McManus, Grain Size Determination and Interpretation. In: Techniques in Sedimentology (ed. T. Maurice) (Blackwell Science,

1995) 63-85.

[21]. G. M. Friedman, Dynamic Processes and Statistical parameters compared for size Frequency Distribution of Beach and River

Sands, Journal of Sedimentary Petrolology, 37, 1967, 327-354.

[22]. R. J. Moiola, and D. Weiser, Textural Parameters: An Evaluation, Journal of Sedimentary Petrology, 38, 1968, 45- 53.

[23]. E. Sneed and R. Folk, Pebbles in the Lower Clolorado River, Texas: a Study in Particle Morphogenesis, Journal of Geology, 66,

1958, 114-150.

Use of Statistical Parameters in the Sedimentological ...

Documents

Transcript of Use of Statistical Parameters in the Sedimentological ...